This invention relates generally to internal combustion engines, and more particularly to exhaust gas recirculation systems in such engines.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment.
EGR systems primarily recirculate exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, further reducing the emission of exhaust gas byproducts which would be emitted as undesirable pollutants from the internal combustion engine.
Some internal combustion engines include turbochargers to increase engine performance and are available in a variety of configurations. When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted by a poppet-type EGR valve directly from the exhaust manifold. The percentage of the total exhaust flow which is diverted for reintroduction into the intake manifold of an internal combustion engine is known as the EGR rate of the engine.
The recirculated exhaust gas is preferably introduced to the intake airstream downstream of the compressor and air-to-air aftercooler (ATAAC). Introducing the exhaust gas downstream of the compressor and ATAAC is preferred in some systems due to reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 issued to Brett M. Bailey, the inventor of the present invention, on Sep. 8, 1998, and assigned to the assignee of the present invention.
The reintroduction of exhaust gases will occur naturally when the exhaust manifold pressure is higher than the turbocharger boost pressure. However, when such a turbocharged engine operates under low speed and high torque conditions, the boost pressure is typically higher than the exhaust manifold pressure and recirculation of the exhaust gases is not possible. Early approaches to address this problem have included using devices such as back pressure valves, restrictive turbines, throttle valves, and venturi inlet systems. Each can be used to improve the back pressure to boost pressure gradient to some degree, but each approach results in increased fuel consumption.
A problem with any EGR system is to inject the right amount of EGR across the operating range of the engine. If too much EGR is added, the air/fuel ratio will drop into the high teens, producing considerable particulate emissions. Relatively expensive devices, such as air mass flow sensors, are generally required to determine the amount of EGR. These devices add additional expense to the cost of the engine and an increased chance of system failure considering the high number of miles and hours that on-road vehicles, particularly diesel powered vehicles, operate. If the EGR rate can be controlled, the next problem is in cooling the exhaust to allow the most EGR dilutent in the inlet charge. If the cooling is accomplished by a jacket water cooler, all of the thermal energy of the EGR is transmitted into the engine""s cooling system, which is already stressed by the increased rejection resulting from the higher charge temperatures caused by the EGR. Thus, the high temperatures and corrosiveness of exhaust gases flowing through the EGR line make the job of cooling the exhaust very difficult. High temperatures, and worse yet, high thermal gradients, make the job of sealing the multitude of pipes and passages of the heat exchangers next to impossible for long-term reliability and durability.
Previous methods of cooling the EGR involve a heat exchanger, for example the aforementioned jacket water cooler, to reduce the temperature of the EGR. Typical heat exchangers allow soot to build up inside the cooler, thereby increasing the pressure drop across the cooler. The engine has no ability to overcome or clear the barrier of soot forming within the passages. As the passages become clogged, there will be less and less EGR flowing into the intake manifold of the engine unless sophisticated computer controls and sensors are used to determine a change in air flow through the engine, or other determination of engine performance. Also, the exhaust of a diesel engine, in particular, contains particulate matter or soot that can build up on surfaces. The particulate matter or soot typically contains sulfuric acid that is highly corrosive to many metals. Thus, the EGR path must be made of materials that are corrosion resistant so as to keep leaks from forming. The material of choice has been stainless steel, which is significantly more expensive than steel or cast iron.
The present invention is directed to overcoming one or more of the problems set forth above.
In accordance with one aspect of the present invention, an internal combustion engine includes a block having at least one combustion chamber defined therein, an intake manifold in fluid communication with the combustion chamber, and a first exhaust manifold fluidly connected to the combustion chamber for transporting exhaust gas therefrom to at least one of a first primary exhaust outlet and a first EGR exhaust outlet. The engine further includes a first check valve having an inlet fluidly coupled to the first EGR exhaust outlet, a regenerator directional control valve having an inlet ports, first and second bidirectional flow ports and a bleed air discharge port. The inlet port is in fluid communication with the outlet of the check valve. The engine further includes first and second stationary regenerators, each having a first end and a second end. The first ends of the stationary regenerators are in fluid communication with a respective one of the bidirectional flow ports of the regenerator directional flow control valve. The second ends of the stationary regenerators are in selective communication with either the intake manifold of the engine or said bleed flow line that is in fluid communication with the intake manifold.
In another aspect of the present invention, an EGR system for an internal combustion engine which has a block defining a plurality of combustion chambers, an intake manifold, and an exhaust manifold arranged for transporting exhaust gas from at least one of the combustion chambers through at least one of a first primary exhaust outlet and a first EGR exhaust outlet. The EGR system includes a first check valve having an inlet fluidly coupled to the first EGR exhaust outlet of the exhaust manifold, and a regenerator directional flow control valve having an inlet port, first and second bidirectional flow ports, and a bleed air discharge port. The inlet port of the regenerator directional flow control valve is in fluid communication with the outlet of the check valve. The engine further includes first and second stationary regenerators, each having a first end and a second end. The first ends of the stationary regenerators are in respective fluid communication with one of the bidirectional flow ports of the regenerator directional flow control valve. The second ends of the stationary generators are in selective communication with either the intake manifold of the engine or said bleed flow line that is in fluid communication with the intake manifold.
Yet another aspect of the present invention includes a method for using an EGR system with an internal combustion engine. The internal combustion engine has a plurality of combustion chambers, an intake manifold, and an exhaust manifold, and the EGR system includes a check valve having an inlet end fluidly coupled to an EGR exhaust outlet of the exhaust manifold of the engine, a regenerator directional flow control valve, and first and second stationary regenerators. The method includes the steps of operating the EGR system in first and second modes in response to selective positioning of the regenerator directional flow control valve. Operating the EGR system in the first mode includes selectively moving the regenerator directional flow control valve to a first position whereby exhaust gas discharged through the EGR exhaust outlet of the exhaust manifold is directed to the first stationary regenerator, whereupon the temperature of the recirculated exhaust gas is reduced and then introduced into a conduit in communication with the intake manifold of the engine. Simultaneously, bleed air from the conduit in fluid communication with the intake manifold is directed through the second stationary regenerator, thereby cooling the second recuperator, then directed through the regenerator directional flow control valve to the exhaust manifold of the engine. Subsequently, the EGR system is operated in the second mode in response to moving the regenerator directional flow control valve to a second position, whereupon recirculated exhaust gas received from the EGR exhaust outlet of the exhaust manifold is directed by the regenerator directional flow control valve to the second stationary recuperator and then, after being cooled during passage through the second regenerator, is directed to the conduit in fluid communication with the intake manifold. Simultaneously during the second mode operation, bleed air from the conduit in fluid communication with the intake manifold is directed through the first stationary recuperator, thereby cooling the first stationary recuperator, and thence directed by the regenerator directional flow control valve to the exhaust manifold of the engine.